Chang Kee Lee

UV-curable semi-interpenetrating polymer network-integrated, highly bendable plastic crystal composite electrolytes for shape-conformable all-solid-state lithium ion batteries

A facile approach to fabricate a highly bendable plastic crystal composite electrolyte (PCCE) for use in shape conformable all-solid-state lithium-ion batteries is demonstrated. This strategy is based on integration of a semi-interpenetrating polymer network (semi-IPN) matrix with a plastic crystal electrolyte (PCE, 1 M lithium bis-trifluoromethanesulfonimide in succinonitrile). In comparison to conventional carbonate-based electrolytes, salient benefits of the PCE are the thermal stability and nonflammability, which show promising potential as a safer electrolyte. The semi-IPN matrix in the PCCE is composed of a UV (ultraviolet)-crosslinked ethoxylated trimethylolpropane triacrylate polymer network and polyvinylidene fluoride-co-hexafluoropropylene (as a linear polymer). Solid electrolyte properties of the PCCE are investigated in terms of plastic crystal behavior, mechanical bendability, and ionic transport. Owing to the presence of the anomalous semi-IPN matrix, the PCCE exhibits unprecedented improvement in bendability, along with affording high ionic conductivity. Based on this understanding of the PCCE characteristics, feasibility of applying the PCCE to solid electrolytes for lithium-ion batteries is explored. The facile ionic transport of the PCCE, in conjunction with suppressed growth of cell impedance during cycling, plays a crucial role in providing excellence in cell performance. These advantageous features of the PCCE are further discussed with an in-depth consideration of the semi-IPN matrix architecture and its specific interaction with the PCE.

All-inkjet-printed, solid-state flexible supercapacitors on paper

The forthcoming ubiquitous innovations driven by flexible/wearable electronics and Internet of Things (IoT) have inspired the relentless pursuit of advanced power sources with versatile aesthetics. Here, we demonstrate a new class of solid-state flexible power sources that are fabricated directly on conventional A4 paper using a commercial desktop inkjet printer. A salient feature of the inkjet-printed power sources is their monolithic integration with paper, i.e., they look like inkjet-printed letters or figures that are commonly found in office documents. A supercapacitor (SC), which is composed of activated carbon/carbon nanotubes (CNTs) and an ionic liquid/ultraviolet-cured triacrylate polymer-based solid-state electrolyte, is chosen as a model power source to explore the feasibility of the proposed concept. Cellulose nanofibril-mediated nanoporous mats are inkjet-printed on top of paper as a primer layer to enable high-resolution images. In addition, CNT-assisted photonic interwelded Ag nanowires are introduced onto the electrodes to further improve the electrical conductivity of the electrodes. The inkjet-printed SCs can be easily connected in series or parallel, leading to user-customized control of cell voltage and capacitance. Notably, a variety of all-inkjet-printed SCs featuring computer-designed artistic patterns/letters are aesthetically unitized with other inkjet-printed images and smart glass cups, underscoring their potential applicability as unprecedented object-tailored power sources.

Heterolayered, One-Dimensional Nanobuilding Block Mat Batteries

The rapidly approaching smart/wearable energy era necessitates advanced rechargeable power sources with reliable electrochemical properties and versatile form factors. Here, as a unique and promising energy storage system to address this issue, we demonstrate a new class of heterolayered, one-dimensional (1D) nanobuilding block mat (h-nanomat) battery based on unitized separator/electrode assembly (SEA) architecture. The unitized SEAs consist of wood cellulose nanofibril (CNF) separator membranes and metallic current collector-/polymeric binder-free electrodes comprising solely single-walled carbon nanotube (SWNT)-netted electrode active materials (LiFePO4 (cathode) and Li4Ti5O12 (anode) powders are chosen as model systems to explore the proof of concept for h-nanomat batteries). The nanoporous CNF separator plays a critical role in securing the tightly interlocked electrode-separator interface. The SWNTs in the SEAs exhibit multifunctional roles as electron conductive additives, binders, current collectors and also non-Faradaic active materials. This structural/physicochemical uniqueness of the SEAs allows significant improvements in the mass loading of electrode active materials, electron transport pathways, electrolyte accessibility and misalignment-proof of separator/electrode interface. As a result, the h-nanomat batteries, which are easily fabricated by stacking anode SEA and cathode SEA, provide unprecedented advances in the electrochemical performance, shape flexibility and safety tolerance far beyond those achievable with conventional battery technologies. We anticipate that the h-nanomat batteries will open 1D nanobuilding block-driven new architectural design/opportunity for development of next-generation energy storage systems.

Compliant polymer network-mediated fabrication of a bendable plastic crystal polymer electrolyte for flexible lithium-ion batteries

We demonstrate a bendable plastic crystal polymer electrolyte (referred to as “B-PCPE”) for use in flexible lithium-ion batteries. The B-PCPE proposed herein is composed of a plastic crystal electrolyte (PCE, 1 M lithium bis-trifluoromethanesulphonimide (LiTFSI) in succinonitrile (SN)) and a UV (ultraviolet)-cured polymer network bearing long linear hydrocarbon chains (here, trimethylolpropane propoxylate triacrylate (TPPTA) polymer is exploited). The solid electrolyte characteristics of the B-PCPE are investigated in terms of plastic crystal behavior, mechanical bendability, ionic conductivity, and cell performance. Owing to the presence of long linear hydrocarbon chains attached to crosslinkable acrylate groups, the TPPTA polymer network in the B-PCPE acts as a compliant mechanical framework, thereby exerting a beneficial influence on bendability and also interfacial resistance with lithium metal electrodes. Meanwhile, the B-PCPE exhibits slightly lower ionic conductivity than a control sample (referred to as “R-PCPE”) incorporating a rigid and stiff polymer network of ethoxylated trimethylolpropane triacrylate (ETPTA). This unique behavior of the B-PCPE is discussed with an in-depth consideration of the polymer network structure and its specific interaction with the lattice defect phase of SN in the PCE. Although relatively sluggish ionic transport is observed in the B-PCPE, its intimate interfacial contact with electrodes (possibly due to the mechanically compliant TPPTA polymer network) may beneficially contribute to imparting satisfactory cycling performance.

A shape-deformable and thermally stable solid-state electrolyte based on a plastic crystal composite polymer electrolyte for flexible/safer lithium-ion batteries

A solid-state electrolyte with reliable electrochemical performance, mechanical robustness and safety features is strongly pursued to facilitate the progress of flexible batteries. Here, we demonstrate a shape-deformable and thermally stable plastic crystal composite polymer electrolyte (denoted as “PC-CPE”) as a new class of solid-state electrolyte to achieve this challenging goal. The PC-CPE is composed of UV (ultraviolet)-cured ethoxylated trimethylolpropane triacrylate (ETPTA) macromer/close-packed Al2O3 nanoparticles (acting as the mechanical framework) and succinonitrile-mediated plastic crystal electrolyte (serving as the ionic transport channel). This chemical/structural uniqueness of the PC-CPE brings remarkable improvement in mechanical flexibility and thermal stability, as compared to conventional carbonate-based liquid electrolytes that are fluidic and volatile. In addition, the PC-CPE precursor mixture (i.e., prior to UV irradiation) with well-adjusted rheological properties, via collaboration with a UV-assisted imprint lithography technique, produces the micropatterned PC-CPE with tunable dimensions. Notably, the cell incorporating the self-standing PC-CPE, which acts as a thermally stable electrolyte and also a separator membrane, maintains stable charge/discharge behavior even after exposure to thermal shock condition (=130 °C/0.5 h), while a control cell assembled with a carbonate-based liquid electrolyte and a polyethylene separator membrane loses electrochemical activity.

Multifunctional semi-interpenetrating polymer network-nanoencapsulated cathode materials for high-performance lithium-ion batteries

As a promising power source to boost up advent of next-generation ubiquitous era, high-energy density lithium-ion batteries with reliable electrochemical properties are urgently requested. Development of the advanced lithium ion-batteries, however, is staggering with thorny problems of performance deterioration and safety failures. This formidable challenge is highly concerned with electrochemical/thermal instability at electrode material-liquid electrolyte interface, in addition to structural/chemical deficiency of major cell components. Herein, as a new concept of surface engineering to address the abovementioned interfacial issue, multifunctional conformal nanoencapsulating layer based on semi-interpenetrating polymer network (semi-IPN) is presented. This unusual semi-IPN nanoencapsulating layer is composed of thermally-cured polyimide (PI) and polyvinyl pyrrolidone (PVP) bearing Lewis basic site. Owing to the combined effects of morphological uniqueness and chemical functionality (scavenging hydrofluoric acid that poses as a critical threat to trigger unwanted side reactions), the PI/PVP semi-IPN nanoencapsulated-cathode materials enable significant improvement in electrochemical performance and thermal stability of lithium-ion batteries.

Homogeneous decoration of zeolitic imidazolate framework-8 (ZIF-8) with core–shell structures on carbon nanotubes

Considerable attention has focused on the combination of carbon nanotubes (CNTs) and metal–organic frameworks (MOFs) since both nanomaterials have outstanding properties. We describe a method for the homogeneous decoration of a MOF (ZIF-8 was chosen) onto the surfaces of CNTs dispersed by polyvinylpyrrolidones (PVPs) in methanol, which was revealed by a scanning electron microscopic study. The homogeneous coating of the MOF on the CNTs, and nanostructures of the CNT-MOF were controlled by simply changing the concentrations of the MOFs. Furthermore, this method was also applicable to graphene and graphene oxide (GO). CO2 uptakes of the CNT-MOF and graphene-MOF were significantly improved as compared to the nonhomogeneous composites synthesized without the PVP functionalization, and a good reproducibility of the CO2 adsorption was confirmed by the cycling test.

One-pot surface engineering of battery electrode materials with metallic SWCNT-enriched, ivy-like conductive nanonets

A longstanding challenge facing energy conversion/storage materials is their low electrical conductivity, which often results in unwanted sluggish electrochemical reactions. Here, we demonstrate a new class of one-pot surface engineering strategy based on metallic single-walled carbon nanotube (mSWCNT)-enriched, ivy-like conductive nanonets (mSC nanonets). The mSC nanonets are formed on the surface of electrode materials through a poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO)-assisted sonication/filtration process. PFO is known as a dispersant for SWCNTs that shows a higher affinity for semiconducting SWCNTs (sSWCNTs) than for mSWCNTs. Driven by this preferential affinity of PFO, sSWCNTs are separated from mSWCNTs in the form of sSWCNT/PFO hybrids, and the resulting enriched mSWCNTs are uniformly deposited on electrode materials in the form of ivy-like nanonets. Various electrode materials, including lithium-ion battery cathodes/anodes and perovskite catalysts, are chosen to explore the feasibility of the proposed concept. Due to their ivy-like conductive network, the mSC nanonets increase the electronic conductivity of the electrode materials without hindering their ionic transport, eventually enabling significant improvements in their redox reaction rates, charge/discharge cyclability, and bifunctional electrocatalytic activities. These exceptional physicochemical advantages of the mSC nanonets, in conjunction with the simplicity/versatility of the one-pot surface engineering process, offer a new and facile route to develop advanced electrode materials with faster electrochemical reaction kinetics.